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Thanks Andy, great stuff. I think we can be pretty
sure it was as you suggested and not aircraft.
If it was aircraft it would be there all the time
presumably.
Pete and I plan to repeat the test when we can,
probably next week, will let you know if we see the same thing
again.
Vy 73,
Chris, G4AYT.
----- Original Message -----
Sent: Friday, March 04, 2011 7:18
PM
Subject: LF: Topband ionogram trace
Here's Peter's update on the 'unusual' topband split trace.
Might explain its cleanliness
Andy
---------- Forwarded message ---------- From: Peter Martinez <[email protected]>Date: 4 March
2011 18:35 Subject: Re: Dopplergrams 12 years ago To: Andy Talbot < [email protected]> Andy: I had a
look at the QRSS sample that G4AYT captured. Around the same time I was
watching the signal from the Fairford ionosonde. This sweeps from 1625kHz,
through top-band and on up to 13MHz. At that time it was clear that the Fcrit
was getting down towards 2MHz so the F-layer was rising rapidly so this would
have been responsible for the increasing negative Doppler shift he was seeing
on one of the traces. In fact the MUF on the Fairford-Kendal path dropped
below 1.7MHz at about 3 am that night. There was also evidence of night-time
sporadic-E. This is sometimes known as Auroral sporadic E but it isn't
'auroral' in the sense we usually mean, but refers to patches of Es which
drift south from the Auroral oval, probably initiated by the same particle
precipitation that causes aurora. This Es activity could have been responsible
for the non-Doppler-shifted trace that G4AYT saw. On a normal night only the
F-layer would be reflecting on top-band. Fairford now has a new
ionosonde equipment, a Digisonde DPS-4D which I find is much easier to
'eavesdrop' on. The Digisondes are pulse sounders with the receiver co-located
with the transmitter with the receiver synchronised to the transmitter
locally. They didn't need to be locked to anything and they weren't stable.
The new one behaves rather better, stepping exactly 25kHz exactly every 640mS
(locked to GPS). I have my system stepping in sync and have some crude
ionograms already and have confirmed that the pulse timing is accurate and
stable. The next job is to implement the pulse-compression algorithm, which is
very similar to that used by LORAN C. This will give me real-time
ionograms again, a facility I lost when the UK chirpsounders closed down last
year.
73 Peter ----- Original Message ----- From: "Andy
Talbot" < [email protected]> To: < [email protected]> Sent: Thursday, March
03, 2011 7:59 PM Subject: Dopplergrams 12 years ago
Hi Peter - Cast your mind back. We did some of the first
Dopplergram tests on 1967kHz back in 1998, and produced the plots
shown http://www.g4jnt.com/Download/1967jnt1.jpghttp://www.g4jnt.com/Download/1967jnt3.jpghttp://www.g4jnt.com/Download/1967jnt4.jpgCan you
recall the vertical span on the trace? As far as I recall,
your EVM software decimated from 8kHz, then you set 80% of the samplinbg
rate as plot BW, so 3.125, 6.25Hz etc But t'would be
interesting to know for sure. Someone on the LF reflector (see
below) has just posted the plot of some QRSS topband tests, and was
"surprised" to see the trace splitting. So I looked out these to
show what was done over a decade ago. Andy On 3 March
2011 18:55, Chris < [email protected]> wrote:
Hi All,
Yesterday evening Pete, M0FMT,
transmitted QRSS on topband for a test. An
unexpected effect was
noticed with the trace splitting in two. Nothing new
or 'earth
shattering' I expect, but new to us and worthy of
further
experimentation.
See the result and conclusion on my website
http://qsl.net/g4ayt on
the
bottom of page 1.
I have never seen this effect on 137, even
with quite strong audible
signals, maybe others have.
Vy
73,
Chris, G4AYT, Whitstable,
UK.
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